Ablation probe with echogenic insulative sheath

ABSTRACT

Tissue ablation probes are provided. Each tissue ablation probe comprises an electrically conductive probe shaft, at least one tissue ablation electrode carried by a distal end of the probe shaft, and an electrically insulative outer sheath disposed on the probe shaft. The sheath is at least partially composed of polyether ether ketone (PEEK) and another material comprising condensed-phase particles interspersed throughout the PEEK to increase the echogenicity of the outer sheath. The durability of the PEEK allows the sheath to be formed as thinly as possible, thereby minimizing the diameter of the ablation probe, while the inclusion of condensed-phase particles within the PEEK does not significantly degrade the durability of the sheath.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/878,794, now allowed, filed on Sep. 9, 2010, which itself is acontinuation of U.S. patent application Ser. No. 11/456,034, now issuedas U.S. Pat. No. 7,799,022, filed on Jul. 6, 2006. The above-notedApplications are incorporated by reference as if set forth fully herein.

FIELD OF THE INVENTION

The field of the invention relates generally to the structure and use ofradio frequency (RF) ablation probes for the treatment of tissue.

BACKGROUND OF THE INVENTION

The delivery of radio frequency (RF) energy to target regions withinsolid tissue is known for a variety of purposes of particular interestto the present invention. In one particular application, RF energy maybe delivered to diseased regions (e.g., tumors) for the purpose ofablating predictable volumes of tissue with minimal patient trauma.

RF ablation of tumors is currently performed using one of two coretechnologies. The first technology uses a single needle electrode, whichwhen attached to a RF generator, emits RF energy from an exposed,uninsulated portion of the electrode. The second technology utilizesmultiple needle electrodes, which have been designed for the treatmentand necrosis of tumors in the liver and other solid tissues. U.S. Pat.No. 6,379,353 discloses such a probe, referred to as a LeVeen NeedleElectrode™, which comprises a cannula and an electrode deployment memberreciprocatably mounted within the delivery cannula to alternately deployan electrode array from the cannula and retract the electrode arraywithin the cannula. Using either of the two technologies, the energythat is conveyed from the electrode(s) translates into ion agitation,which is converted into heat and induces cellular death via coagulationnecrosis. The ablation probes of both technologies are typicallydesigned to be percutaneously introduced into a patient in order toablate the target tissue.

In the design of such ablation probes, which may be applicable to eitherof the two technologies, RF energy is often delivered to an electrodelocated on a distal end of the probe's shaft via the shaft itself. Thisdelivery of RF energy requires the probe to be electrically insulated toprevent undesirable ablation of healthy tissue. In the case of a singleneedle electrode, all but the distal tip of the electrode is coated withan electrically insulative material in order to focus the RF energy atthe target tissue located adjacent the distal tip of the probe. In thecase of a LeVeen Needle Electrode™, RF energy is conveyed to the needleelectrodes through the inner electrode deployment member, and the outercannula is coated with the electrically insulative material to preventRF energy from being transversely conveyed from the inner electrodedeployment member along the length of the probe.

The procedure for using the ablation probe requires the insulativecoating to have sufficient durability. To illustrate, when designing RFablation probes, it is desirable to make the profile of the probe shaftas small as possible, namely to have a smaller gauge size, in order tominimize any pain and tissue trauma resulting from the percutaneousinsertion of the probe into the patient. Thus, it is advantageous forthe electrically insulative material applied to the probes be as thin aspossible. However, RF ablation probes are often introduced through othertightly toleranced devices that may compromise the integrity of thethinly layered insulation, thereby inadvertently exposing healthy tissueto RF energy.

For example, probe guides are often used to point ablation probestowards the target tissue within a patient. A typical probe guide takesthe form of a rigid cylindrical shaft (about 1-2 inches in length) thatis affixed relative to and outside of a patient, and includes a lumenthrough which the ablation probe is delivered to the target tissue. Tomaximize the accuracy of the probe alignment, it is desirable that theguide lumen through which the probe is introduced be about the same sizeas the outer diameter of the probe, thereby creating a tight tolerancebetween the probe and the probe guide. As another example, ablationprobes are also often used with co-access assemblies that allow severaldifferent devices, such as ablation probes, biopsy stylets, and drugdelivery devices, to be serially exchanged through a single deliverycannula. To minimize pain and tissue trauma, it is desirable that theprofile of the delivery cannula be as small as possible. To achievethis, the lumen of the delivery cannula will typically be the same sizeas the outer diameter of the ablation probe, thereby creating a tighttolerance between the probe and the delivery cannula.

As a result, during the initial introduction of the probe through adelivery device, such as a probe guide or cannula of a co-access system,it is possible that a portion of the insulation may shear off as theprobe is introduced through the delivery device. Consequently, theattending physician will either have to replace the probe with a new oneor risk ablating healthy tissue. Thus, the durability of the insulativecoating is critical to prevent damaging healthy tissue and/or having todiscard the probe.

Besides providing the insulation on the ablation probe with thenecessary durability, it is also necessary to ensure that the distal endof the ablation probe, where the RF energy will be directed, is incontact with the target tissue. This may be achieved with an imagingdevice located outside the patient's body, such as an ultrasound imager.The echogenicity of the probe determines how well the probe may belocated using ultrasound techniques. That is, the more echogenetic theablation probe, the easier it is to determine the location of the probewith ultrasound imaging and to ensure accurate contact with the targettissue.

To achieve greater echogenicity, it is known in the art, for example, tomake marks or nicks along the shaft in order to increase the amount ofedges and surfaces on the shaft, thereby creating a non-uniform surfaceprofile. Echogenicity increases as the number of edges and surfaces forreflecting the ultrasound is increased. This technique may also beapplied to insulative coating on the probe shaft. It is also known inthe art to have air bubbles interspersed throughout the insulativecoating in order to increase echgenicity. However, the inclusion of airbubbles may degrade the integrity of the insulative coating, which mayalso occur when marks or nicks are made in the insulative coating.

Therefore, there is a need in the art for an ablation probe with aninsulative coating having improved echogenicity for properly positioningthe ablation device relative to the target tissue, while also havingsufficient durability and size to remain intact during insertion and useof the ablation probe.

SUMMARY OF THE INVENTION

In accordance with the present inventions, tissue ablation probes areprovided. Each tissue ablation probe comprises an electricallyconductive probe shaft, at least one tissue ablation electrode carriedby a distal end of the probe shaft, and an electrically insulative outersheath disposed on the probe shaft. The ablation probe may, e.g., beaffixed to, or deployable from, the distal end of the probe shaft. Inone embodiment, the outer sheath is fixably disposed on the probe shaft,although in other embodiments, the outer sheath may be slidably disposedon the probe shaft. The ablation probe may further comprise anelectrical connector carried by a proximal end of the probe shaft,wherein the electrical connector is electrically coupled to the tissueablation electrode(s) through the probe shaft. In accordance with thepresent inventions, a method of ablating tissue comprises introducingthe tissue ablation probe through a delivery device into a tissue region(e.g., percutaneously), and ablating the tissue region with the at leastone tissue ablation electrode.

In accordance with a first aspect of the present inventions, the sheathis at least partially composed of a polyether ether ketone (PEEK).Although the present inventions should not be so limited in theirbroadest aspects, the durability of the PEEK allows the sheath to beformed as thinly as possible, thereby minimizing the diameter of theablation probe. In an optional embodiment, tissue ablation probe mayfurther comprise particles distributed through the PEEK to increase theechogenicity of the tissue ablation probe. In one embodiment, theparticles are solid, so that the durability of the sheath is notdegraded. However, because the PEEK provides the sheath with maximumdurability, in some embodiments, the particles may be gel or liquidparticles, and even gas particles, without significantly degrading thedurability of the sheath.

In accordance with a second aspect of the present inventions, the sheathis at least partially composed of a base material and another materialinterspersed throughout the base material to increase the echogenicityof the outer sheath. The other material comprises condensed-phaseparticles (such as, solid particles, gel particles, or liquidparticles). While the present inventions should not be so limited intheir broadest aspects, the use of condensed-phase particles may ensurethat the durability of the outer sheath is not significantly degradedeven if a conventional insulative material (e.g., a non-PEEK material)is used as the base material. The other material may optionally beinterspersed in non-uniform portions and/or non-uniform locations in thebase material. The other material may also be composed of more than onesubstance if desired.

In accordance with a third aspect of the present inventions, the sheathis at least partially composed of polyether ether ketone (PEEK) andanother material comprising condensed-phase particles interspersedthroughout the PEEK to increase the echogenicity of the outer sheath.Although the present inventions should not be so limited in theirbroadest aspects, the durability of the PEEK allows the sheath to beformed as thinly as possible, thereby minimizing the diameter of theablation probe, while the inclusion of condensed-phase particles withinthe PEEK does not significantly degrade the durability of the sheath.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, the presentinventions.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention, in which similar elements are referred to bycommon reference numerals. In order to better appreciate how theabove-recited and other advantages of the present inventions areobtained, a more particular description of the present inventionsbriefly described above will be rendered by reference to specificembodiments thereof, which are illustrated in the accompanying drawings.Understanding that these drawings depict only typical embodiments of theinvention and are not therefore to be considered limiting of its scope,the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is a plan view of a tissue ablation system arranged in accordancewith one embodiment of the present inventions;

FIG. 2 is a side view of a tissue ablation probe used in the tissueablation system of FIG. 1;

FIGS. 3A-3B illustrate cross-sectional views of the tissue ablationprobe of FIG. 2, taken along the line 3-3;

FIG. 4 is a perspective view of another tissue ablation probe that canbe used within the tissue ablation system of FIG. 1, wherein anelectrode array is particularly shown retracted;

FIG. 5 is a perspective view of the tissue ablation probe of FIG. 4,wherein the electrode array is particularly shown deployed;

FIGS. 6A-6B illustrate cross-sectional views of the tissue ablationprobe of FIGS. 4 and 5, taken along the line 7-7;

FIGS. 7A-7B illustrate cross-sectional views of one method of using thetissue ablation system of FIG. 1 to treat tissue; and

FIGS. 8A-8B illustrate cross-sectional views of another method of usingthe tissue ablation system of FIG. 1 to treat tissue.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to FIG. 1, a tissue ablation system 10 constructed inaccordance with one embodiment of the present inventions, will now bedescribed. The tissue ablation system 10 generally comprises an ablationprobe 12 configured for introduction into the body of a patient forablative treatment of target tissue, a source of ablation energy, and inparticular a radio frequency (RF) generator 14, and a cable 16electrically connecting the ablation probe 12 to the RF generator 14.

Referring now to FIG. 2, the ablation probe 12 will be described infurther detail. The ablation probe 12 comprises an elongated, probeshaft 18 having a proximal end 20 and a distal end 22. The probe shaft18 is composed of an electrically conductive material, such as stainlesssteel. The probe shaft 18 has a suitable length, typically in the rangefrom 5 cm to 30 cm, preferably from 10 cm to 25 cm, and an outerdiameter consistent with its intended use, typically being from 0.7 mmto 5 mm, usually from 1 mm to 4 mm.

The ablation probe 12 further comprises an electrically insulative outersheath 24 disposed on the probe shaft 18. In the illustrated embodiment,the sheath 24 is affixed to the probe shaft 18, and may be applied tothe probe shaft 18 using any suitable means. For example, the insulativeouter sheath 24 can be applied to the probe shaft 18 as a heat shrink orcan be extruded onto the probe shaft 18.

The sheath 24 is composed of a base material 50 that is electricallyinsulative with sufficient durability to be inserted into a probe guide.One preferred material for the base material 50 is polyether etherketone (PEEK). In one embodiment of the invention, the sheath 24 extendsthe entire length of the probe shaft, with the exception of a distal tipof the probe shaft 18. In this manner, an RF ablation electrode 26 isformed by the exposed portion of the distal tip.

In one embodiment, the sheath 24 may be composed entirely of the basematerial 50, in particular PEEK, as shown in FIG. 3A. Preferably,however, the sheath 24 may additionally comprise a second material 51interspersed throughout the base material 50, as shown in FIG. 3B.Notably, for purposes of illustration, the particle size of the secondmaterial 51 is shown as being much greater than the actual size of theparticles. The second material 51 has a density that is different fromthat of the base material 50, such that the sheath 24 varies in density.As shown in FIG. 3B, the addition of the second material 51 may alsovary the surface profile of the sheath 24. Thus, it can be appreciatedthat the presence of the second material 51 causes the echogenicity ofthe ablation probe 12 to be greater than what would result with the basematerial 50 alone.

The second material 51 is preferably composed of condensed phaseparticles, i.e. solid, gel, or liquid particles. Examples of condensedphase particles composing the second material 51 are glass, sand, orcrystal particles. Alternatively, the second material 51 may be composedof a gas, although the use of gas particles may decrease the durabilityof the sheath 24. In this case, it is desirable that the base material50 be composed of a highly durable and electrically insulative material,such as PEEK, such that the physical integrity of the sheath 24 ismaintained. The second material 51 may also be composed of more than onetype of particle. For example, the second material 51 may be composed ofboth glass particles and gel particles.

The second material 51 may be interspersed throughout the base material50 in uniform or non-uniform portions. Additionally, the second material51 may be interspersed throughout the base material in a uniform patternor non-uniform manner. For example, it may be more cost-effective if thesecond material 51 is produced such that the particles composing thesecond material 51 vary considerably in size, as opposed to maintaininga narrow size range for the particles. In addition, instead of havingthe second material 51 added uniformly to the base material 50, it maybe more efficient, and cost-effective, to simply mix particles of thesecond material 51 into the base material 50 such that the secondmaterial 51 is randomly dispersed throughout the base material 50 whenit is applied to the probe shaft 18.

The distal tip of the probe shaft 18 is a tissue-penetrating tip, whichallows the ablation probe 12 to be more easily introduced throughtissue, while minimizing tissue trauma. The RF ablation electrode 26located at the distal tip may be affixed to the distal end 22 of theprobe shaft 18, or it may be deployable from the probe shaft 18. Theprobe shaft 18 is preferably composed of a rigid or semi-rigid material,such that the ablation probe 12 can be introduced through solid tissueto a target tissue site. Alternatively, the ablation probe 12 may beintroduced through the tissue with the aid of a cannula and trocarassembly, in which case, the probe shaft 18 may be composed of aflexible material, and the distal end 22 may be blunted.

The ablation probe 12 further comprises a handle 34 mounted to theproximal end 20 of the probe shaft 18. The handle 34 is preferablycomposed of a durable and rigid material, such as medical grade plastic,and is ergonomically molded to allow a physician to more easilymanipulate the ablation probe 12. The handle 34 comprises an electricalconnector 36 with which the cable 16 (shown in FIG. 1) mates.Alternatively, the RF cable 16 may be hardwired within the handle 34.The electrical connector 36 is electrically coupled to the ablationelectrode 26 via the probe shaft 18, with the insulative sheath 24operating to focus RF energy at the electrode 26 where the targetedtissue presumably lies.

In the illustrated embodiment, the RF current is delivered to theelectrode 26 in a monopolar fashion, which means that current will passfrom the electrode 26, which is configured to concentrate the energyflux in order to have an injurious effect on the surrounding tissue, anda dispersive electrode (not shown), which is located remotely from theelectrode 26 and has a sufficiently large area (typically 130 cm² for anadult), so that the current density is low and non-injurious tosurrounding tissue. The dispersive electrode may be attached externallyto the patient, e.g., using a contact pad placed on the patient's flank.

Referring back to FIG. 1, the RF generator 14 may be a conventionalgeneral purpose electrosurgical power supply operating at a frequency inthe range from 300 kHz to 9.5 MHz, with a conventional sinusoidal ornon-sinusoidal wave form. Such power supplies are available from manycommercial suppliers, such as Valleylab, Aspen, Bovie, and Ellman. Mostgeneral purpose electrosurgical power supplies, however, are constantcurrent, variable voltage devices and operate at higher voltages andpowers than would normally be necessary or suitable. Thus, such powersupplies will usually be operated initially at the lower ends of theirvoltage and power capabilities, with voltage then being increased asnecessary to maintain current flow. More suitable power supplies will becapable of supplying an ablation current at a relatively low fixedvoltage, typically below 200 V (peak-to-peak). Such low voltageoperation permits use of a power supply that will significantly andpassively reduce output in response to impedance changes in the targettissue. The output will usually be from 5 W to 300 W, usually having asinusoidal wave form, but other wave forms would also be acceptable.Power supplies capable of operating within these ranges are availablefrom commercial vendors, such as Boston Scientific TherapeuticsCorporation. Preferred power supplies are models RF-2000 and RF-3000,available from Boston Scientific Corporation.

Referring now to FIGS. 4 and 5, another tissue ablation probe 52 thatcan be used in conjunction with the RF generator 14 to create analternative tissue ablation system will be described. The tissueablation probe 52 includes an elongated cannula 54 and an inner probeshaft 56 slidably disposed within the cannula 54. The cannula 54includes an elongate shaft 58 having a proximal end 60, a distal end 62,and a central lumen 64 (shown in FIGS. 6A-6B), and an electricallyinsulative sheath 66 (shown in Fig. FIGS. 6A-6B) disposed on the cannulashaft 58.

The cannula shaft 58, itself, is composed of an electrically conductivematerial, such as stainless steel. The material from which the cannulashaft 58 is composed is preferably a rigid or semi-rigid material, suchthat the ablation probe 52 can be introduced through solid tissue to atarget tissue site. The distal end 62 of the cannula shaft 58 comprisesa tissue-penetrating tip 68, which allows the ablation probe 52 to bemore easily introduced through tissue, while minimizing tissue trauma.Alternatively, the ablation probe 52 may be introduced through thetissue with the aid of another cannula and trocar assembly, in whichcase, the cannula shaft 58 may be composed of a flexible material, andthe distal end 62 may be blunted. The cannula shaft 58 has a suitablelength, typically in the range from 5 cm to 30 cm, preferably from 10 cmto 25 cm, and an outer diameter consistent with its intended use,typically being from 0.7 mm to 5 mm, usually from 1 mm to 4 mm.

In the illustrated embodiment, the insulative sheath 66 is affixed tothe cannula shaft 58, and may be applied to the cannula shaft 58 usingany suitable means, e.g., as a heat shrink or extrusion. The insulativesheath 66 has a composition similar to that of the insulative sheath 24described above. In particular, as best shown in FIGS. 6A-6B, theinsulative sheath 66 is composed of a base material 70, in particularPEEK, as shown in FIG. 6A. Preferably, as described earlier in respectto FIGS. 3A and 3B, the sheath 66 additionally comprises a secondmaterial 71 interspersed throughout the base material 70, as shown inFIG. 6B. Notably, for purposes of illustration, the particle size of thesecond material 71 is shown as being much greater than the actual sizeof the particles. As discussed earlier, the second material 71 has adensity that is different from that of the base material 70, such thatthe sheath 66 varies in density. As shown in FIG. 6B, the addition ofthe second material 71 may also vary the surface profile of the sheath66. The base material 70 and the second material 71 provide similaradvantages as those discussed above with respect to the base material 50and the second material 51 in the sheath 24. That is, the base material70 and the second material 71 increase the echogenicity of the ablationprobe 52 such that the probe 52 may be more precisely located usingultrasound imaging.

The inner probe shaft 56 is slidably disposed within the cannula lumen64 and has a proximal end 76 and a distal end 78, and an array ofelectrode tines 80 carried by the distal end 78 of the probe shaft 56.Like the cannula shaft 58, the inner probe shaft 56 is composed of anelectrically conductive material, such as stainless steel. The innerprobe shaft 56 is composed of a suitably rigid material, so that it hasthe required axial strength to be slide within the cannula lumen 64.

The ablation probe 52 further includes a handle assembly 82, whichincludes a handle member 84 mounted to the proximal end 76 of the innerprobe shaft 56, and a handle sleeve 86 mounted to the proximal end 60 ofthe cannula 54. The handle member 84 is slidably engaged with the handlesleeve 86 (and the cannula 54). The handle member 84 and handle sleeve86 can be composed of any suitable rigid material, such as, e.g., metal,plastic, or the like. The handle assembly 82 also includes an electricalconnector 88 mounted within the handle member 84. The electricalconnector 88 is electrically coupled to the electrode array 80 via theinner probe shaft 56, with the insulative sheath 66 operating to focusRF energy at the electrode array 80 where the targeted tissue presumablylies. The electrical connector 88 is configured for mating with theproximal end of the RF cable 16 (shown in FIG. 1). Alternatively, the RFcable 16 may be hardwired within the handle member 84. Like the previousdescribed ablation probe 52, RF current may be delivered to theelectrode array 80 in a monopolar fashion.

It can be appreciated that longitudinal translation of the probe shaft56 relative to the cannula 54 in a distal direction 90 can be achievedby holding the handle sleeve 86 and displacing the handle member 84 inthe distal direction 90, thereby deploying the electrode array 80 fromthe distal end 62 of the cannula shaft 58 (FIG. 5), and longitudinaltranslation of the probe shaft 56 relative to the cannula 54 in aproximal direction 92 can be achieved by holding the handle sleeve 86and displacing the handle member 84 in the proximal direction 92,thereby retracting the probe shaft 56 and the electrode array 80 intothe distal end 62 of the cannula 54 (FIG. 4).

Further details regarding electrode array-type probe arrangements aredisclosed in U.S. Pat. No. 6,379,353, which is hereby expresslyincorporated by reference.

Having described the structure of the tissue ablation system 10, itsoperation in treating targeted tissue will now be described. Thetreatment region may be located anywhere in the body where hyperthermicexposure may be beneficial. Most commonly, the treatment region willcomprise a solid tumor within an organ of the body, such as the liver,kidney, pancreas, breast, prostrate (not accessed via the urethra), andthe like. The volume to be treated will depend on the size of the tumoror other lesion, typically having a total volume from 1 cm³ to 150 cm³,and often from 2 cm³ to 35 cm³. The peripheral dimensions of thetreatment region may be regular, e.g., spherical or ellipsoidal, butwill more usually be irregular. The treatment region may be identifiedusing conventional imaging techniques capable of elucidating a targettissue, e.g., tumor tissue, such as ultrasonic scanning, magneticresonance imaging (MRI), computer-assisted tomography (CAT),fluoroscopy, nuclear scanning (using radiolabeled tumor-specificprobes), and the like. Preferred is the use of high resolutionultrasound of the tumor or other lesion being treated, eitherintraoperatively or externally.

Referring now to FIGS. 7A-7B, the operation of the tissue ablationsystem 10 is described in treating a treatment region TR with tissue Tlocated beneath the skin or an organ surface S of a patient. Theablation probe 12 is first introduced through the tissue T under theguidance of a conventional ultrasound imaging device, so that theelectrode 26 is located at a target site TS within the treatment regionTR, as shown in FIG. 7A. This can be accomplished using any one of avariety of techniques. In the preferred method, a delivery device, suchas a probe guide 94, is used to guide the ablation probe 12 towards thetarget site TS. In particular, the probe guide 94 is affixed and alignedrelative to the target site TS, and the ablation probe 12 is introducedthrough the probe guide 94. Facilitated by the sharpened distal tip, theablation probe 12 is percutaneously introduced through the patient'sskin until the electrode 26 is located in the treatment region TR.

As discussed above, the echogenicity of the sheath 24 will allow theuser to more precisely locate the ablation probe 12 using ultrasoundimaging. This will help to ensure direct contact of the ablation probe12 with the treatment region and to minimize damage to surroundinghealthy tissue.

Once the ablation probe 12 is properly positioned, the cable 16 of theRF generator 14 (shown in FIG. 1) is then connected to the electricalconnector 36 of the ablation probe 12, and then operated to transmit RFenergy to the electrode 26, thereby ablating the treatment region TR, asillustrated in FIG. 7B. As a result, a lesion L will be created, whichwill eventually expand to include the entire treatment region TR.

Alternatively, if the ablation probe 52 illustrated in FIGS. 4 and 5 isused, the cannula 54 can be introduced through the probe guide 94 untilthe distal end 62 of the cannula 54 is located at the target site TS,after which the inner probe shaft 56 can be distally advanced throughthe cannula 54 to deploy the electrode array 80 out from the distal end62 of the cannula 54, as shown in FIG. 8A.

As previously discussed, once the ablation probe 52 is properlypositioned, the cable 16 of the RF generator 14 (shown in FIG. 1) isthen connected to the electrical connector 88 of the ablation probe 52,and then operated to transmit RF energy to the electrode 26, therebyablating the treatment region TR, as illustrated in FIG. 8B. As aresult, a lesion L will be created, which will eventually expand toinclude the entire treatment region TR.

Although particular embodiments of the present inventions have beenshown and described, it will be understood that it is not intended tolimit the present inventions to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present inventions. Thus, the present inventions are intended tocover alternatives, modifications, and equivalents, which may beincluded within the spirit and scope of the present inventions asdefined by the claims.

1. A method of operating a tissue ablation system comprising:introducing an electrically conductive probe shaft through tissue, theelectrically conductive probe shaft having at least one electrode and anelectrically insulative outer sheath at least partially comprisingpolyether ether ketone (PEEK) disposed over the probe shaft and aplurality of particles distributed through the PEEK, wherein theechogenicity of the tissue ablation probe is increased by the inclusionof the particles; imaging the electrically conductive probe shaft withan ultrasound imaging device during introduction of the electricallyconductive probe shaft; placing the at least one electrode at a targetsite within the tissue; and ablating tissue by delivery of RF energythrough the at least one electrode.
 2. The method of claim 1, whereinthe particles comprise solid particles.
 3. The method of claim 1,wherein the particles comprise liquid particles.
 4. The method of claim1, wherein the particles comprise gas particles.
 5. The method of claim1, wherein the particles are interspersed through the outer sheath in auniform manner.
 6. The method of claim 1, wherein the particles areinterspersed through the outer sheath in a non-uniform manner.
 7. Themethod of claim 1, wherein introducing the electrically conductive probeshaft through tissue comprises inserting a probe guide into the tissueand introducing the electrically conductive probe shaft through theprobe guide.
 8. The method of claim 1, wherein the tissue comprises oneof liver tissue, kidney tissue, pancreas tissue, breast tissue, andprostate tissue.
 9. A method of operating a tissue ablation systemcomprising: introducing an electrically conductive elongated cannulathrough tissue, the electrically conductive elongated cannula having anelectrically insulative outer sheath at least partially comprisingpolyether ether ketone (PEEK) disposed over the elongated cannula and aplurality of particles distributed through the PEEK, wherein theechogenicity of the elongated cannula is increased by the inclusion ofthe particles; imaging the electrically conductive elongated cannulawith an ultrasound imaging device during introduction of theelectrically conductive elongated cannula; inserting a probe shaftthrough the electrically conductive elongated cannula so as to place atleast one electrode operatively coupled to the probe shaft at a targetsite within the tissue; and ablating tissue by delivery of RF energythrough the at least one electrode.
 10. The method of claim 9, whereinthe particles comprise solid particles.
 11. The method of claim 9,wherein the particles comprise liquid particles.
 12. The method of claim9, wherein the particles comprise gas particles.
 13. The method of claim9, wherein the particles are interspersed through the outer sheath in auniform manner.
 14. The method of claim 9, wherein the particles areinterspersed through the outer sheath in a non-uniform manner.
 15. Themethod of claim 9, wherein the tissue comprises one of liver tissue,kidney tissue, pancreas tissue, breast tissue, and prostate tissue.